This invention relates to high voltage electrolytic capacitors utilizing metal electrodes, particularly aluminum foil electrodes, in the presence of an electrolyte comprising ethylene glycol, ammonium pentaborate and its mixtures with boric acid. Such type of electrolyte is commonly referred to as a glycol-borate electrolyte. Glycol-borate electrolytes are well-known in the art and are described in U.S. Pat. Nos. 3,646,403; 3,351,823; and 3,302,071. In these electrolytes, some of the dissolved borates react with the glycol to form glycol-borate esters and water. The concentration of water from this reaction may be about 10% by weight of electrolyte, but can be adjusted to a desired level by heating the electrolyte or by adding water. Use of such glycol-borate electrolytes usually have been limited to operating conditions of approximately 450 volts and 85.degree. C.
Typically, an electrolytic capacitor comprises metal anode and cathode members separated by a paper spacer impregnated with an electrolyte. The anode and cathode are provided with tabs for making electrical connections thereto. The electrolytic capacitor is usually constructed in the form of a roll enclosed in a leakproof outer container. Such a typical electrolytic capacitor construction is taught in the drawing of U.S. Pat. No. 3,646,403.